Many types of imaging systems, such as flat panel displays and non-thermal, direct marking print heads require bi-directional drive of many high voltage elements. These imaging systems typically have arrays of imaging elements that form images on displays or on print surfaces by selective turning on and off the imaging elements. High-voltage output transistors generally control the on or off state of the elements by selectively connecting them to either a positive or a negative high voltage supply rail, or to neither.
Generally, low-voltage signals, relative to the driving signals for the imaging elements, control the timing and state of the drive signals. Display and print head driving controllers, or chips, receive relatively low-voltage serial digital bit streams of image data and convert them to parallel data of 96 to 640 bits wide. The driver chips then translate the levels of the low-voltage signals to track the high voltage supply rails and use those level-translated signals to switch high-voltage output transistors that control the on and off state of the imaging elements.
The terms ‘low-voltage’ and ‘high-voltage’ used here relate to each other. A ‘low-voltage’ signal is one used to drive the logic circuitry, generally between 2.5 and 5 V. A ‘high-voltage’ signal is one that is higher than the voltage used to drive the logic circuitry, such as signals between 10 and 100 V.
Existing driver chips use high-voltage transistors in DC coupled configurations to accomplish this level translation. These high-voltage transistors typically require large isolation areas around each transistor, therefore requiring large areas of the chip substrate such as silicon, increasing the cost of the chip.
One solution lies in the use of capacitively coupled level translation that requires less area and therefore enables lower cost chips. However, existing capacitively coupled isolation circuits generally take up too much area and are too complex to fits hundreds of copies on a single chip.